Induction heating apparatus for fusing vitreous enamel



E. J. LIMPEL Aug 19, 1958 Filed Feb. 1, 1954 a m mw mm 2 Ni. w i i Z W:fi T 4 Z e a, A G 2 6 m. H 2 v 0 o u m. E B 6 fl E 7 n 2 H United StatesPatent INDUCTION HEATING APPARATUS FOR FUSIN G VITREOUS ENAMEL Eugene J.Limpel, Fox Point, Wis.,. assignor to 0. Smith Corporation, Milwaukee,Wis., a corporation of New York Application February 1, 1954, Serial No.407,546

8 Claims. (Cl. 21910.49)

This invention relates to an induction heating appatus for firing avitreous enamel coat-ing on a steel article.

The use of induction heating for fusing a vitreous enamel .coating onsteel has been shown .to have several advantages over furnace firing inthat the heat is developed in the steel article itself due to thecurrent induced therein and any gases driven .out .of the steel onheating can escape through the coating before it reaches a moltencondition. In furnace firing, the outside surface .or .coating isinitially heated so that gases driven off from the steel have to passthrough the molten coating and are apt to form boiling defects inthecoating.

The present invention is .directed to an induction heating apparatus forprogressively firing a vitreous enamel coating on a hollow metalarticle, such as a pipe or a smokestack, whereby the power requirementsare substantially reduced .due to the use of heat reflective surfaces incombination with the induction coils.

According to the invention an induction heating coil is disposedadjacent the coated steel article and spaced out of contact therewith..By energizing the ,coil, a current is induced in the article to heatthe same to a temperature sufiicient to fuse the vitreous .enamelcoating to the article.

To reduce .the heat loss through radiation, a heat reflective member isdisposed in spaced relation between the article and the coil. The memberis formed with a polished heat reflective surface facing the article sothat heat radiated from the article will .be reflected back toward thesame.

To prevent the reflective surface from oxidizing and losing its polishedcondition, a cooling jfluid is introduced into contact with the surfaceof the reflective member adjacent the coil and is directedlongitudinally along the surface to the ends of the coil. At the ends ofthe .coil the reflective member is bent outwardly to deflect the fluidaway from the coated article and prevent the stream of fluid fromdisfiguring the coating.

In a second embodiment of the invention the induction coil is formedwith a generallyvcylindrical surface facing the article. The surface ispolished and serves to reflect the heat back toward the .articlein amanner similar "to 'that of the reflective member of the firstembodiment.

By use of the reflective surface, the heat loss is substantially reducedand this results in a considerable reduction-in power requirements.

The drawing furnished herewith illustrates the best mode presentlycontemplated of carrying out the invention set forth hereinafter.

Figure 1 is a vertical section of the induction heating apparatusshowing the heating of a tubular member;

Fig. 2 is a fragmentary transverse section taken on line 2-2 of Figurel; and

Fig. 3 is a fragmentary vertical section of a modified form of theinduction heating apparatus.

2,848,566 Patented Aug. 19, 1958 The induction heating apparatuscomprises a base 1 which supports a generally annular frame 2. Anannular, hollow, helically wound induction heating coil 3 is disposedwithin frame 2 and is supported by brackets 4 which extend inwardly fromframe 2.

The base 1 is provided with an opening 5 which is axially aligned withframe 2 and coil 3. A pipe 6 or other metal article to be fired isadapted to be drawn upwardly from opening 5 through coil 3.

The pipe 6 is coated on the inner and outer surfaces with a vitreousenamel or glass frit 7 which is to be progressively heated and fused tothe steel pipe as the pipe moves upwardly within coil 3.

The pipe 6 is moved upwardly in relation to coil 3 by any conventionalapparatus. As shown in Figure l, a chain hoist 8 is attached to abracket 9 welded to the upper end of pipe 6 and upward movement of chainhoist 8 draws the pipe upwardly through coil 3.

To maintain alignment of pipe 6 within opening 5 as the pipe is movedtherethrough suitable guides, not shown, may be associated with theopening.

As shown in Figure 1, .the coil 3 may consist of two axially alignedsections zconnected electrically in series to provide in effect a singlecontinuous coil.

Current is applied .to the coil 3 through lines 10 and the current incoil 3 induces a current in the portion of pipe 6 passing within thecoil to heat the same. A temperature in the range of 1560" F. to 1600 F.is required to fuse the enamel 7 to thesteel pipe. The temperaturedeveloped in pipe @6 is determined by the current applied to the coiland the number of coil turns.

To cool the coil 3, a cooling :fluid such as water is introduced intoone end of each sectionof the coil through conduit 11 and withdrawn fromthe opposite end of the coil throughconduit 12.

The turns of coil 3 are insulated from each other by an insulatingmaterial 13, such as resin impregnated cotton tape, which is wrappedaround the .coil turns and baked at an elevated temperature for anextended period. The material 13 functions to provide an insulatedspacing between theturns of the coil 3.

As the heat developed Within the portion of pipe 6 passing through thecoil 3 tends to radiate to surrounding objects having a lessertemperature, particularly the coil 3 and frame 2, a plurality ofindependent generally curved reflectors 14 are disposed in a spacedrelation within coil 3. Reflectors 14 are .in a concentric relation withcoil 3 and serve to reduce :the radiation heat'loss.

The reflectors 14 are formed as a series of separate curved sectionsrather than as a continuous tubular member so as to prevent anyappreciable current from being induced therein. A high temperatureinsulating material may be disposed in the gaps between the adjacentedges of the reflectors.

Reflectors 14 are spaced radially outward of the pipe 6, and the innersurface of reflectors '14 facing the pipe is polished or otherwise:treated to provide a mirror-like reflecting surface.

The reflectors 14 extendlongitudinally:beyond.theends of coil 3 .and:the ends of the reflectors are connected to frame 2 by bolts or thelike to secure the reflectors in position within the coil.

To space reflectors 14 from coil 3 a sheet of an insulating material'15, such as asbestos paper, 'is disposed on the .inner surfaceof thecoil 3.

The reflectors 14 are made of ametal, such as aluminum .or silveror goldplated steel, which will withstand high temperature and can be polished:to .a highly reflective condition. To lprevent oxidation of thereflective surface at high temperatures, the reflectors should becooled. As shown .in Figure 1 cooling fluid, such :as air, is introducedfrom a supply conduit 16 into a 2h0ll0W =discharge ring 17 which isdisposed outwardly between the sections of coil 3. The inner peripheryof ring 17 is provided with a plurality of circumferentially spacedopenings 18 through which the fluid is discharged against the outersurface of reflectors 14. The insulating sheet 15 is interrupted at theposition of ring 17 to permit the flow of fluid against the reflectors.

To permit the fluid to pass longitudinally of reflectors 14 to eitherend thereof, the reflectors are formed with a series of longitudinallyextending corrugations. The fluid discharged from ring 17 passeslongitudinally of the reflectors through a series of circumferentiallyspaced longitudinal passages 19, defined by the corrugations ofreflectors 14 and insulating sheet 15, to the ends of the reflectors tocool the same.

To deflect the fluid away from the coated pipe and eliminate thepossible disfigurement of the coating by the stream of fluid, the endsof the reflectors 14 are bent or flared outwardly, as shown at 20.

In operation, the pipe 6 is initially coated with the vitreous enamel 7by spraying, dipping or the like. The coated pipe is then disposedwithin opening and the chain hoist 8 is connected to the bracket 9.

Current is applied to the coil and the pipe is then slowly drawnupwardly through coil 3 by operation of the hoist to progressively firethe coated pipe and fuse the coating to the steel throughout the lengthof the pipe.

The article may be progressively fired from the bottom up or from thetop down as desired.

It has been found that applying a current of about 3000 amperes to acoil having 10 turns resulted in the article or pipe being heated to atemperature of about 1550 F., thereby producing a very satisfactoryfusion of the coating to the pipe. The speed of movement of the pipe wasabout 5 per minute.

The present invention may be applied to the firing of a vitreous enamelcoating on either the inner surface or outer surface or both surfaces ofa hollow article. Similarly the induction coil may be disposed either onthe outside of the article or on the inside of the article to fire thecoating on either or both surfaces of the article.

In addition, to progressively fire the coating it is necessary thatthere be relative movement between the article and the coil. Thisrelative movement may be accomplished by moving the article in respectto coil, as disclosed in the above description, or conversely, by movingthe coil in respect to the article.

A second embodiment of the invention is shown in Fig. 3. In thisembodiment a hollow, helically wound induction coil 21 is carried byframe 2 and is disposed in axial alignment with opening 5 in position toreceive the pipe 6 in a manner similar to that of the first embodiment.

A cooling fluid is introduced into the hollow interior of coil 21through a conduit 22 and withdrawn from the coil through conduit 23.

The turns of the coil are insulated from each other by an insulatingmaterial 24, such as asbestos or transite, which is disposed between theturns.

The heat radiated from the pipe is reflected back toward the same byproviding the inner portion of the coil 21 with a generally cylindricalsurface, indicated by 25. In cross section each turn of the coil has agenerally flat face facing the pipe. The surface 25 is a heat reflectivesurface formed by polishing the coil or metal plating the same.

The surface 25 functions similarly to the reflectors 14 of the firstembodiment. However, as the reflective surface is a part of the coilitself, the cooling fluid flowing through the hollow interior of thecoil serves to cool the surface 25 and prevent oxidation thereof.

To increase the reflective surface area, a pair of reflective rings 26are secured to the frame at the ends of the coil 21 and in effectincrease the length of the reflective surface.

The reflective surface of rings 26 is made of highly polished aluminumor silver, gold or copper plated steel, and the rings are suitablysecured to frame 2 to maintain the rings in position with respect to thecoil.

In operation the apparatus of Fig. 3 functions similarly to that of thefirst embodiment with the pipe being moved through the coil toprogressively heat the pipe to a temperature in the range of 1500 F. to1600 F. to fuse the enamel to the pipe.

The reflective surfaces of coil 21 serve to reduce the radiation lossesof heat and increase the effectiveness of the firing by reducing thepower requirements.

Various modes of carrying out the invention are contemplated as withinthe scope of the following claims particularly pointing out anddistinctly claiming the subject matter which is regarded as theinvention.

I claim:

1. Apparatus for firing a vitreous enamel to a steel article, comprisingan induction heating element, means to energize said element and inducea current in said article to heat the same to a temperature sufficientto fuse the vitreous enamel coating to the steel article, means forreflecting the heat radiated from the article back toward the article,said metal being selected from the group consisting of aluminum, silver,gold and copper and means to cool the reflective surface to preventoxidation and tarnishment thereof.

2. Apparatus for progressively firing a vitreous enamel coating on thesurface of a steel article, comprising an induction heating coil toreceive the article, means to energize said coil and induce a current insaid article to heat the same to a temperature suflicient to fuse thevitreous enamel coating to the steel article, means associated with theinner surface of the coil and disposed generally concentric to the axisofthe coil for reflecting the heat radiated from the article back towardthe article, said metal being selected from the group consisting ofaluminum, silver, gold and copper, means to cool the reflective surfaceto prevent oxidation and tarnishment thereof, and means for impartingrelative movement between the coil and the article to effect aprogressive heating and fusing of the enamel to the article throughoutthe length of said article.

3. Apparatus for firing a vitreous enamel coating on the inner and outersurface of a tubular member, comprising an annular induction heatingcoil to receive the tubular member, means to energize the coil andinduce a current in said member to heat the same above the temperaturerequired for the fusion of the vitreous enamel coating to the member, aheat reflective metal surface selected from the group consisting ofaluminum, silver, gold and copper and disposed on the inner face of saidcoil concentric to the axis of the coil and extending coextensively inan axial direction with the coil and being highly polished to reflectthe heat radiated by said member back toward the same, and means forcooling said reflective surface to prevent oxidation and tarnishmentthereof.

4. Apparatus for firing a vitreous enamel coating on a steel articlewhich comprises, an induction heating coil, means to energize said coiland induce a current in said article to heat the same to a temperaturesufiicient to fuse the vitreous enamel coating to the steel article, aheat reflective metal member selected from the group consisting ofaluminum, copper, gold and silver and disposed inwardly of the coil andhaving a heat reflective inner surface facing away from said coil toreflect heat radiated from the article back toward the same, means forintroducing a gaseous cooling medium into contact with the outer surfaceof said member adjacent the coil and directing said mediumlongitudinally along said last named surface to cool said member andprevent oxidation of the heat reflective surface, and means associatedwith said member and disposed at an end of the coil for directing thegaseous medium away from the article to prevent the medium fromcontacting the coating on said article.

5. Apparatus for firing a vitreous enamel coating on a steel articlewhich comprises, an induction heating coil disposed adjacent the articleand spaced therefrom, means to energize said coil and induce a currentin said article to heat the same to a temperature suflicient to fuse thevitreous enamel coating to the steel article, a heat reflective memberdisposed in spaced relation between the coil and the article and havinga heat reflective surface facing said article to reflect heat radiatedfrom the article back toward the same, said member being formed with aplurality of generally longitudinal grooves and having an end thereofprojecting longitudinally beyond the corresponding end of said coil withthe projecting end of said member being bent away from the article, andmeans for introducing a cooling medium into contact with the surface ofsaid member adjacent the coil and directing said medium through saidgrooves to the bent end ofsaid member with said bent end serving todirect the medium away from the coated article, and said medium servingto cool the member and prevent oxidation of the reflective surface.

6. Apparatus for firing a vitreous enamel coating on the inner and outersurfaces of a tubular steel article, comprising an induction heatingcoil disposed concentrically of the article and spaced outwardlythereof, means to energize said coil and induce a current in saidarticle to heat the same to a temperature suflicient to fuse thevitreous enamel coating to the steel article, a heat reflective memberdisposed in spaced relation between the coil and the article and havinga heat reflective surface facing said article to reflect heat radiatedfrom the article back toward the same, an insulating material disposedbetween the coil and said reflective member, said member having aplurality of generally longitudinally extending grooves in the outersurface thereof adjacent said insulating material and said memberextending longitudinally beyond the ends of said coil with the ends ofsaid member being bent away from said article, and an annular supplymember carrying a cooling medium and having a plurality of outletsdisposed to direct said cooling medium between the windings of said coilagainst the outer surface of said reflective member, said medium passinglongitudinally through said grooves to the ends of said member to coolthe member and prevent oxidation of the reflective surface and beingdeflected away from the article by the bent ends of said member toprevent the medium from contacting the coating thereon.

7. Apparatus for firing a vitreous enamel to a steel.

article, comprising a hollow induction heating element with a surface ofsaid element being formed with an exposed generally flat configurationin an axial direction to define a heat reflective metal surface, saidsurface being highly polished and being selected from the groupconsisting of aluminum, copper, gold and silver and serving to reflectheat radiated from the article back toward the same, means to energizesaid element and induce a current in said article to heat the same to atemperature sufficient to fuse the vitreous enamel coating to the steelarticle, and means to introduce a cooling medium into the hollowinterior of said element to cool the same and prevent oxidation of thereflective surface.

8. Apparatus for progressively firing a vitreous enamel coating on theinner and outer surface of a tubular article, comprising a hollowinduction heating coil formed of a plurality of turns and adapted toreceive said article, the inner portion of each turn of said coil facingsaid article being provided with an exposed generally flat configurationin an axial direction and defining a heat reflective metal surfaceselected from the group consisting of aluminum, copper, gold and silver,means to energize said coil and induce a current in the article to heatthe same to a temperature sufficient to fuse the vitreous enamel coatingto the steel article, means to introduce a cooling medium into thehollow interior of said coil to cool the same and prevent oxidation ofthe reflective surface, a pair of generally cylindrical reflective metalmembers disposed in axial alignment with the coil at either end thereof,said heat reflective surface and said reflective members serving toreflect the heat radiated from the article back toward the same toincrease the effectiveness of the heating operation, and means forimparting relative movement between the coil and the article to effect aprogressive heating and fusing of the enamel to the article throughoutthe length of said article.

References Cited in the file of this patent UNITED STATES PATENTS1,321,492 Thornton, Jr. Nov. 11, 1919 1,431,997 Unger Oct. 17, 19221,981,629 Northrup Nov. 20, 1934 1,997,761 Bailey et al Apr. 16, 19352,040,767 Dudley May 12, 1936 2,202,758 Denneen et al May 28, 19402,672,550 Vaughan Mar. 16, 1954 2,676,234 Lackneret et al Apr. 20, 19542,687,464 Crawford Aug. 24, 1954 2,730,599 Ronay Jan. 10, 1956 2,781,437McArthur Feb. 12, 1957 FOREIGN PATENTS 310,458 Great Britain Nov. 20,1929 645,387 Germany May 26, 1937

1. APPARATUS FOR FIRING A VITREOUS ENAMEL TO A STEEL ARTICLE, COMPRISINGAN INDUCTION HEATING ELEMENT, MEANS TO ENERGIZE SAID ELEMENT AND INDUCEA CURRENT IN SAID ARTICLE TO HEAT THE SAME TO A TEMPERATURE SUFFICIENTTO FUSE THE VITREOUS ENAMEL COATING TO THE STEEL ARTICLE, MEANS FORREFLECTING THE HEAT RADIATED FROM THE ARTICLE BACK TOWARD THE ARTICLE,SAID METAL BEING SELECTED FROM